High-frequency waveguide feed in combination with a short-backfire antenna

ABSTRACT

A high-frequency waveguide feed in combination with a shortbackfire antenna having a cavity and multiple reflectors to permit high power handling capabilities and high frequency applications. An open end of a waveguide is used as the primary radiator in the antenna cavity. The waveguide intrudes into the cavity from behind the larger reflector plate. The polarization response of the antenna is determined by the type of waveguide chosen.

United States Patent Ehrenspeck et al.

[ Nov. 20, 1973 HIGH-FREQUENCY WAVEGUIDE FEED IN COMBINATION WITH A SHORT-BACKFIRE ANTENNA Inventors: Hermann W. Ehrenspeck, Belmont;

John A. Strom, Nabnasett, both of Mass.

The United States of America as represented by the Secretary of the Air Force, Washington, DC.

Filed: Oct. 4, 1972 Appl. No.: 295,078

Assignee:

US. Cl. 343/779, 343/781, 343/837 Int. Cl. H0lq 19/14 Field oi Search 343/779, 781, 837

References Cited UNITED STATES PATENTS 2/ 1964 Ehrenspeck 343/887 Primary Examiner-Eli Lieberman Att0rneyl-larry A. Herbert, Jr. et al.

[57] ABSTRACT A high-frequency waveguide feed in combination with a short-backfire antenna having a cavity and multiple reflectors to permit high power handling capabilities and high frequency applications. An open end of a waveguide is used as the primary radiator in the antenna cavity. The waveguide intrudes into the cavity from behind the larger reflector plate. The polarization response of the antenna is determined by the type of waveguide chosen.

17 Claims, 9 Drawing Figures PATENTEI] W20!!!" SHEET 1 [IF HIGH-FREQUENCY WAVEGUIDE FEED IN COMBINATION WITH A SHORT-BACKFIRE ANTENNA BACKGROUND OF THE INVENTION This invention relates to reflector antennas of the short-backfire type described in U.S. Pat. Nos. 3,438,043 and 3,508,278, which were issued Apr. 8, 1969 and Apr. 21, 1970, respectively, to Hermann W. Ehrenspeck. The specific invention is a feed system that improves the performance of short-backfire antennas and arrays of short-backfire antennas for frequencies above 1 GHZ.

A typical short-backfire antenna is comprised of a planar reflector approximately two wavelengths in diameter with a rim along the edge approximately onehalf wavelength deep, a reflector disk of approximately one-half wavelength in diameter, arranged parallel to the large reflector, and a feed located between the two reflectors. The feed may be any type of radiator of small axial extension; for example, a dipole, a pair of crossed dipoles, a loop, or a short helix or spiral. Such feeds are, howevr, disadvantageous and impractical for frequencies above approximately 1 GHz, because their small physical dimensions demand an extremely accurate feed design with narrow tolerances and allow only limited power handling. It is the object of this invention to avoid these disadvantages by using as short-backfire feed the open end of a waveguide which intrudes into the antenna cavity from behind the reflector.

The combination of the high-frequency feed of the present invention and my aforementioned shortbackfire antenna provides a high-frequency, high gain, high-power antenna for ground, aircraft, and space application. A flush-mounted antenna is also provided for speed aircraft and space vehicles. It is also possible to utilize the present invention in arrays for monopulse tracking and telemetry.

SUMMARY OF THE INVENTION A high-frequency waveguide feed in combination with a short-backfire antenna is provided. The combination makes possible an antenna substantially improving high-frequency applications and high power handling capabilities. The short-backfire antenna is of the type hereinbefore mentioned in my U.S. Patents wherein there is included a cavity and multiple reflectors. The feed is comprised of a waveguide, the open end of which intrudes into the antenna cavity from behind one of the reflectors. The reflector center is provided with a hole approximately of the shape and dimensions of the outside of the waveguide. A flange on the back side of the reflector supports the waveguide so that its open end which is the feed can be moved into the cavity to spacings up to approximately one'half wavelength from the reflector plane. Different types of waveguides may be used with the polarization response of the antenna determined by the polarization characteristics and the energizing system of the waveguide.

DESCRIPTION OF THE DRAWINGS FIG. la shows a front view of a first embodiment of the invention in the form of a rectangular waveguidefed short-backfire antenna;

FIG. 1b is a cross-sectional view of FIG. la;

FIG. 2a shows a front view of a second embodiment in the form of a rectangular waveguide-fed shortbackfire antenna;

FIG. 2b is a cross-sectional view of FIG. 20;

FIG. 3a is a view in perspective: of FIG. la;

FIG. 3b is a view in perspective: of FIG. 2a;

FIG 4a shows a perspective view of a third embodiment in the form of a circular waveguide-fed shortbackfire antenna in accordance with FIG. 30;

FIG. 4b shows a perspective view of a fourth embodiment in the form of a circular waveguide-fed shortbackfire antenna in accordance with FIG. 3b; and

FIG. 5 shows a four-element array with circular waveguide feeds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. la shows an example of a front view of the waveguide-fed short-backfire antenna according to the invention, and FIG. lb shows a cross-section of FIG. 1a. Referring to FIGS. la and 1b, there is shown circular plane reflector M of diameter d,., with a rim B of depth W along its edge, a reflector disk R, concentric with M, and a waveguide G whose open end A is moved into the cavity formed by reflector M and rim B. The plane of A represents the radiating aperture of the waveguide feed. It is located approximately midway between M and R Waveguide G is supported by flange K. Although the radiating aperture A is located at approximately the same spacing S, from reflector M, as, for exhmple, the dipole feed in a conventional shortbackfire, the aperture distribution and consequently the radiation pattern of both antennas are different. This effect is due to the different radiation characteristics of the two feeds. Reflector disk R, may be supported in many different ways, for example, by two rods Q which are connected with rim B. Shown in FIG. 1a as horizontal members, they appear in FIG. lb as small circles on R For linearly polarized waveguide feeds metal rods may be used if they are arranged transverse to the plane of polarization, as shown in FIG. 1a. For crossed polarization, however, the rods Q must be made of nonconducting material.

Another configuration of the waveguide-fed shortbackflre according to the invention is presented in FIGS. 2a and 2b. The letter designations have the same meaning as those in the antenna of FIGS. 10 and lb. The radiating aperature A of the waveguide feed is located in the plane of reflector M. It has been found that the antenna performance can be markedly improved by a second disk R in addition to the first reflector disk R,. Disk R is indicated in FIG. 2a by the dashed circle inside R and shown in FIG. 2b in cross-section. With its diameter about the same as that of R it is arranged approximately midway between A and R As the energy enters the cavity from A it is partially intercepted by disk R and dispersed into the cavity in a manner similar to that of a dipole feed. Disk R serves in the same capacity as in the conventional short-backfire, in creating the resonant cavity needed to control the amplitude-phase distribution in the radiating aperture and to extend it to the outer portions of reflector M and to the rim B. Reflector disk R, may be supported in the same manner as shown in FIG. lb, and R may be connected with R, by a rod T made from metal or nonconducting material. FIGS. 3a and 3b are perspective views of waveguide-fed short-backfire antennas according to the invention as shown in FIGS. 1a and 2a, re-

spectively. g r

I It has been found that the configuration of FIG. 1 covers a wider frequency bandwidth than that of FIG. 2. However, the configuration of FIG. 2 offers some structural advantages since the open end of the waveguide can be tightly connected with the backside of reflector M without the need of flange K.

The short-backfire antennas shown in FIGS. la and 2a use rectangular waveguides as feeds. They limit the antennas to linear polarization response. For circular or crossed polarization response, circular or square waveguides with the feasible polarization response have to be used. FIGS. 4a and 4b are perspective views of short-backfire antennas with circular waveguide feeds, with FIG. 4a showing the configuration according to FIG. 3a and FIG. 4b the configuration according to FIG. 3b.

Waveguide-fed short-backfire antennas according to the invention can also be used as parabolic reflector feeds or flush-mounted into metal bodies without losing their favorable performance characteristics. They can also be tightly sealed by a dielectric plate which covers the open side of the cavity. This plate can in addition serve as support for the reflector disk R, as already described in US. Pat. No. 3,508,278.The entire cavity may also be filled with dielectric material which results in a reduction of the antenna dimensions. At the same time the disks may be simply embedded into the dielectric.

The combination of A and R, of FIG. 1 or that of A, R,, and R of FIG. 2 may be in front of a common reflector used as basic elements for short-backfire arrays of any predetermined size. Since in such multielement arrays the number of feeds is reduced to between onefourth and one-sixth the number of gain-comparable dipole or slot arrays, the construction is markedly simplified. FIG. 5 shows as an example a four-element array with four circular waveguide feeds. Each of the circular waveguide feeds is identical to each other and to that shown in FIG. 4a. One of the four is shown including the same character designations as shown in FIG. 4a. There is, however, shown common reflector M in place of M of FIG. 4a and common rib B in place of rim B of FIG. 41a. Rods Q are utilized to support the disks and are identical to the type of rods shown in FIGS. 1-4

What is claimed is:

l. A high frequency waveguide feed in combination with a short-backfire antenna comprising a full reflector having a hole therethrough ofa preselected dimension, a partial reflector spaced at a preselected distance from said full reflector, the spacing between reflectors being substantially an integral multiple of an electrical half wavelength to produce a resonant cavity thus providing a standing wave such that the field slowly decays from its maximum value on the antenna axis and being everywhere approximately in phase, a waveguide feed of a preselected dimension slightly smaller than said preselected dimension of said hole passing through said hole in said full reflector permitting said open end thereof to intrude into said resonant cavity, the configuration of said waveguide feed determining the polarization of said short-backfire antenna.

2. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 1 further including a reflecting rim surrounding said full reflector, said rim having a preselected width.

3. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 2 further including means connected between said refleeting rim and said partial reflector to support said partial reflector at said preselected distance from said full reflector.

4. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 3 wherein said connecting means is comprised of metal rods utilized only during linear polarization, said metal rods being arranged transverse to the plane of polarization.

5. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 3 where said connecting means is comprised of rods of nonconducting material utilized exclusively during cross polarization.

6. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 1 further including a flange connected to said full reflector to support said waveguide feed.

7. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 1 wherein said waveguide feed is rectangular to provide a first predetermined polarization.

8. A high frequency waveguide in combination with a short backfire antenna as described in claim 2 wherein said waveguide feed is circular to provide a second predetermined polarization.

9. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 3 wherein said open end of said waveguide feed is located approximately midway between said full reflector and said partial reflector.

10. A high frequency waveguide in combination with a short-backfire antenna as described in claim 2 wherein said open end of said waveguide is located in the plane of said full reflector.

11. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 10 further including a second partial reflector approximately of the same dimension of the first utilized partial reflector and positioned approximately midway between said open end of said waveguide and the first utilized partial reflector.

12. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 11 further including support means for said second partial reflector connected between said first utilized partial reflector and said second partial reflector.

13. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 12 wherein said waveguide feed consists of a rectangular configuration.

M. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 12 wherein said backfire feed consists of a circular configuration.

l5. Short-backfire antenna arrays with waveguide feeds comprising a common full reflector having a multiplicity of holes therethrough, each of the holes being of a predetermined dimension, a reflecting rim of preselected width surrounding and connected to said common full reflector, a multiplicity of partial reflectors, means to space each of said reflectors being positioned feeds as described in claim 15 wherein said space means is comprised of rods connected between said partial reflectors and said reflecting rim.

17. Short-backfire antenna arrays with waveguide feeds as described in claim 15 wherein each of said open ends intrudes into an associated resonant cavity at a distance approximately midway between said common reflector and the associated partial reflector. 

1. A high frequency waveguide feed in combination with a shortbackfire antenna comprising a full reflector having a hole therethrough of a preselected dimension, a partial reflector spaced at a preselected distance from said full reflector, the spacing between reflectors being substantially an integral multiple of an electrical half wavelength to produce a resonant cavity thus providing a standing wave such that the field slowly decays from its maximum value on the antenna axis and being everywhere approximately in phase, a waveguide feed of a preselected dimension slightly smaller than said preselected dimension of said hole passing through said hole in said full reflector permitting said open end thereof to intrude into said resonant cavity, the configuration of said waveguide feed determining the polarization of said short-backfire antenna.
 2. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 1 further including a reflecting rim surrounding said full reflector, said rim having a preselected width.
 3. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 2 further including means connected between said reflecting rim and said partial reflector to support said partial reflector at said preselected distance from said full reflector.
 4. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 3 wherein said connecting means is comprised of metal rods utilized only during linear polarization, said metal rods being arranged transverse to the plane of polarization.
 5. A high frequency waveguide feed in combination with a short-backfIre antenna as described in claim 3 where said connecting means is comprised of rods of nonconducting material utilized exclusively during cross polarization.
 6. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 1 further including a flange connected to said full reflector to support said waveguide feed.
 7. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 1 wherein said waveguide feed is rectangular to provide a first predetermined polarization.
 8. A high frequency waveguide in combination with a short backfire antenna as described in claim 2 wherein said waveguide feed is circular to provide a second predetermined polarization.
 9. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 3 wherein said open end of said waveguide feed is located approximately midway between said full reflector and said partial reflector.
 10. A high frequency waveguide in combination with a short-backfire antenna as described in claim 2 wherein said open end of said waveguide is located in the plane of said full reflector.
 11. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 10 further including a second partial reflector approximately of the same dimension of the first utilized partial reflector and positioned approximately midway between said open end of said waveguide and the first utilized partial reflector.
 12. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 11 further including support means for said second partial reflector connected between said first utilized partial reflector and said second partial reflector.
 13. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 12 wherein said waveguide feed consists of a rectangular configuration.
 14. A high frequency waveguide feed in combination with a short-backfire antenna as described in claim 12 wherein said backfire feed consists of a circular configuration.
 15. Short-backfire antenna arrays with waveguide feeds comprising a common full reflector having a multiplicity of holes therethrough, each of the holes being of a predetermined dimension, a reflecting rim of preselected width surrounding and connected to said common full reflector, a multiplicity of partial reflectors, means to space each of said reflectors being positioned opposite to an associated hole and at a preselected distance from said common reflector to form a resonant cavity, and a multiplicity of waveguide feeds, each having a preselected dimension slightly smaller than the preselected dimension of an associated hole and each also having an open end, each of said waveguide feeds passing through an associated hole to permit the open end thereof to intrude into an associated resonant cavity.
 16. Short-backfire antenna arrays with waveguide feeds as described in claim 15 wherein said space means is comprised of rods connected between said partial reflectors and said reflecting rim.
 17. Short-backfire antenna arrays with waveguide feeds as described in claim 15 wherein each of said open ends intrudes into an associated resonant cavity at a distance approximately midway between said common reflector and the associated partial reflector. 